Really good contrast with the text and image. I love the image choice and I really appreciate how the image choice focuses on the character.
The design relates to the concept because it looks like the characters are saying the quotes.
For the desktop size, maybe add more type variety such as changes in font size, font weight, and font style. Also, you could explore a neutral background color.
The image resolution for the 1st postcard is a bit grainy.
For the mobile size, maybe orient the quote to the direction the characters are facing so it’s consistent with the desktop size or you could explore more central compositions.
There is an overlap of text and image on the 2nd postcard. You could also change the text color for the 2nd card as well.
Other possible suggestions could be to add overlays for the mobile size so you could add the text over the image without it competing.